The goal of improving the quality of paper is shared by those in the papermaking industry. Experience enables many papermakers to gauge what is needed to produce a desirable sheet of paper with enhanced quality. However, with many stock samples now involving the use of recycled materials, other natural materials, and newly developed synthetic fibres, and with many new fabrics and machines continually emerging, the papermaking industry is considering unchartered methods in which to make paper of enhanced quality.
In lieu of such opportunity, the gamble of increased costs looms apparent. Not all of such new methods produce a desirable output, and some methods are not worth the expense of experimentation. For instance, some stock samples may have fibres of too short a length to use with a certain fabric. Likewise, some machines produce sheets of inferior quality when used with incompatible stock and/or fabric. Without incurring costly trial runs, the industry is currently without a method for determining the quality that a final sheet would possess if used with a new combination of stock, fabric and machine.
The need to determine the final quality of paper is particularly great for those engaged in providing paper for printing applications. In such an arena, it is important that the quality of the final sheet is suitable for printing. The printer can control the rate of absorption of ink that occurs into the sheet during the printing process, by controlling the mixture and viscosity of the ink itself. However, for any given pass through the printing press, the quality of the ink solution will remain the same and therefore, the quality of the final print will be directly related to the absorption rate of the ink from one area of the sheet to the other. This rate of absorption and the degree to which ink penetrates the sheet, is controlled by the density of the area of the sheet upon which the ink solution falls.
Differences in density on paper if great, often make the sheet flocky or cloudy, as seen when looking through the sheet, impacting on the appearance of print throughout a single sheet. The design of the headbox used in the machine and its performance have the greatest effect on sheet density. This, in combination with turbulence created by stationary elements principally dictate the final large scale sheet formation. Additionally, wire marks on the final sheet caused by the structure of the forming fabric on which the sheet was produced, explain the finer levels of density differences on the paper.
In order to determine density differences, the papermaker must analyze the final product after it has been produced on the machine or after it has gone through the printing phase. Such a method of determining density variations is often costly and does not provide a clear indication of where the problem lies. The papermaker must separately modify those variables such as stock, fabric and even the machine used, until achieving the perfect formation for uniform density. This further increases the cost incurred by the papermaker, which is eventually passed on to the consumer.